The Koau or Koao is an unknown takahē or rail-like bird inhabiting the Marquesas Islands, 1000 kilometres northeast of Tahiti. The Marquesas Islands is a semi-mountainous tropical rainforest covered archipelago and together are about 1000 square kilometres in size.

The first written account of a Koau by a European was by archaeologist and explorer, Thor Heyerdal, who witnessed a Koau on Hiva Oa Island in 1937. Heyerdal and a Marquesan islander named Terai were horseback riding in the center of the island when they saw a chicken-sized, large beaked, green-winged purple bird run along the trail and disappear into some ferns. He went a bit off-trail to see if he could see it again but was unsuccessful.

Upon talking to locals, Heyerdahl was told that it was a somewhat rare flightless bird called the Koau that lived in the rainforests. The Koau was known to be very difficult to catch due to their speed and made burrows in mud to hide their chicks. They primarily ate taro roots, were very skittish, and avoided humans. It likely lives in the mountains due to Heyerdahl’s sighting being located in the centre of Hiva Oa, which is quite mountainous. Another hint suggesting they live in higher altitude areas is their name, which translates to “peak” in Marquesian.

Famous post-impressionist painter Paul Gauguin, who lived in French Polynesia for the latter half of his life illustrated an animal very similar to the koau being attacked by a dog in the corner of his painting The Wizard of Hiva Oa. This is notable, as that was the very island a koau was spotted by Heyerdahl. The koau being attacked by a dog is also intriguing, as many flightless birds native to isolated islands such as the koau, had their population decimated due to dogs and cats being introduced upon arrival by Europeans, which would explain their scarcity. In explorer Francis Mazière’s book Mystérieux Archipel du Tiki, he reports hearing about koaus by both Thor Heyerdahl’s book, but also the islanders themselves. He claimed to have not believed their stories, as he never heard of such a bird resembling the description until reading an article about another, very similar bird that lives in New Zealand, called the Takahē in a magazine (above).

Takahēs are well known for being very elusive, being declared extinct in the 1870s and being rediscovered in 1948. Upon showing a photo of a takahē to the locals, they all pointed at it and claimed the koau looked almost identical, which led Mazière to theorize it to be an unknown bird in the Porphyrio genus, and it turned out he may have been correct. In 1988, 600-year-old bones of a new species of presumably extinct bird in the Porphyrio genus called the Marquesas swamphen was found in Hiva Oa and Tahuata, and was identical in description to the koau, albeit there was no way to find out the colouration.